Shulou(Shulou.com)06/01 Report--

Editor to share with you how to use Octave mathematical technology to deal with audio files, I believe that most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

The third part of our digital audio processing technology covers signal modulation and explains how to perform amplitude modulation (Amplitude Modulation), vibrato effect (Tremolo Effect) and frequency variation (Frequency Variation).

Modulation

Amplitude modulation

As its name implies, the amplitude that affects the sinusoidal signal changes constantly according to the information transmitted. Sine wave is called carrier carrier because it carries a lot of information. This modulation technology is used in many commercial broadcasts and citizen information transmission bands (AM).

Why use amplitude modulation technology?

Modulated emission

Assuming that the channel is a free resource, the antenna can transmit and receive signals. This requires an effective electromagnetic signal transmitting antenna, which should be of the same size as the wavelength of the signal to be transmitted. Many signals, including audio components, are usually at 100 hertz or lower. For these signals, if they are transmitted directly, we need to build antennas up to 300 kilometers long. If the information is loaded into the high-frequency carrier of the 100MHz by signal modulation, the antenna needs only 1 meter (transverse length).

Centralized modulation and multi-channel

Assuming that multiple signals occupy a channel, modulation can place different signals in different frequency domain positions so that the receiver can select the particular signal. Applications that use centralized modulation ("multiplexing") include remote sensing data, stereo FM radios and long-distance calls.

Modulation to overcome equipment limitations

The performance of signal processing devices, such as filters, amplifiers, and devices that can be simply composed of them, depends on the situation of the signal in the frequency domain and the relationship between high-frequency and low-frequency signals. Modulation can be used to transmit signals to locations in the frequency domain where it is easier to meet design requirements. Modulation can also convert a "broadband signal" (a signal with a large proportion of high frequency and low frequency) into a "narrowband" signal.

Audio special effects

Many audio special effects use amplitude modulation technology because of their eye-catching and ease of signal processing. We can say a lot, such as vibrato, chorus, rimming and so on. This practicality is why we pay attention to it.

Vibrato effect

The vibrato effect is the simplest application of amplitude modulation. to achieve this effect, we will change (multiply) the audio signal with a periodic signal, using a sine or something else.

> > tremolo='tremolo.ogg'; > > fs=44100; > > fs=44100; > wo=2*pi*440*t; > > wa=2*pi*1.2*t; > > audiowrite (tremolo, cos (wa). * cos (wo), fs)

This will create a sinusoidal signal that works like a vibrato.

Vibrato in a real audio file

Now we will show the vibrato effect in the real world. First of all, we use audio files that have previously recorded male voice'A'. The signal graph looks like this:

> > [yjingfs] = audioread ('A.ogg'); > > plot (y)

Now we will create a complete sinusoidal signal, using the following parameters:

Increment = 1 frequency = 1.5Hz phase = 0 > > taper 0 > plot (Q) > > q=cos (w); > > plot (Q)

Note: when we create a set of time values, by default, it is rendered in a column format, such as a value of 1 × 220500. In order to multiply such a value, it must be changed to the form of a row (220500 × 1). This is what the tactit (:) command does.

We will create a second file in ogg audio format that contains the following modulated signal:

> > tremolo='tremolo.ogg'; > > audiowrite (tremolo, q.frequency changes)

We can change the frequency to achieve some interesting sound effects, such as original sound distortion, movie sound effects, multiplayer competitions.

The influence of sinusoidal frequency modulation

This is the demonstration code of sinusoidal modulation frequency change, according to the equation:

Y=Ac*Cos (wo*Cos (wo/k))

Here:

Ac = increase wo = fundamental frequency k = scalar divisor > > fm='fm.ogg'; > fs=44100; > > tantalizer1Maple FsG10; > > wimp2mm pirates 442mm; > > audiowrite (fm, cos (cos (wq1500). * w), fs); > > [Yjingfs] = audioread ('fm.ogg'); > > figure (); plot (y)

Signal diagram:

You can use almost any type of periodic function frequency modulation. In this case, we only use a sine function. Please change the frequency of the function boldly, use the compound function, or even change the type of function.

The above is all the contents of the article "how to use Octave Mathematical Technology to process Audio Files". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.